Resin film based polyalkylene carbonate and method for preparing the same

ABSTRACT

The present invention relates to a polyalkylene carbonate-based resin film and a manufacturing method thereof. The polyalkylene carbonate-based resin film according to the present invention has biodegradability and complete combustion decomposability to show environment-friendly feature and rubber-like properties. Therefore, the resin film can be applied to various resin molded products requiring elasticity, and in particular, preferably applied to resin molded products such as disposable groves, disposable containers, and disposable rubber molded products.

TECHNICAL FIELD

The present invention relates to a polyalkylene carbonate-based resinfilm and a manufacturing method thereof.

BACKGROUND OF ART

Recently, there have been widely used disposable resin molded productsincluding disposable gloves, packaging films, disposable containers suchas disposable cups or plates, and rubber molded products used forbuilding materials and automotive interior materials. For example,disposable gloves are hard-to-recycle single-use work gloves, and havebeen consumed mainly for industrial uses in the fields of medicine,chemistry or chemical engineering, and in recent years, used andconsumed in wider range of applications related to sanitation or humanhealth, including foods or cosmetics.

These disposable resin molded products, for example, disposable glovescan be manufactured from various resin materials that are thin andelastic with rubber-like properties, for example, from various resinshaving properties identical or similar to those of rubber such assynthetic polyisoprene, polychloroprene, polyurethane, polyvinylchloride, polystyrene-butadiene-styrene, styrene-isoprene-styrene,silicon, polybutadiene methyl methacrylate, polyacrylonitrile, orpolystyrene-ethylene-butylstyrene.

However, the disposable resin molded products manufactured from thoseresin materials are hard to decompose in an environment-friendly way andtoxic gases emitted due to incomplete combustion when landfilled orincinerated seriously cause environmental pollution.

For that reason, many efforts have been made to manufacture thedisposable resin molded product from various biodegradable resinmaterials. Unfortunately, there has never been developed yet such aresin film that is not only biodegradable but also satisfactory inacquiring rubber-like mechanical properties including elasticity,elongation, or strength necessary to the disposable resin moldedproducts such as disposable gloves or the like.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

Accordingly, the present invention provides a resin film that has notonly rubber-like properties but also biodegradability, thereby having anenvironment-friendly feature.

Further, the present invention provides a method for manufacturing theresin film.

Technical Solution

According to the present invention, provided is a polyalkylenecarbonate-based resin film including resin particles containing apolyalkylene carbonate resin, a first surfactant, and a secondsurfactant, in which the second surfactant concentration is higher atthe core of the particle than at the surface of the particle and thefirst surfactant concentration is higher at the surface of the particlethan at the core of the particle.

Herein, the content of the first surfactant at the core of the resinparticle may be less than 5% by weight, based on the total weight of thefirst surfactant contained in the resin particle. Further, the contentof the first surfactant farther away from half the particle radius fromthe core of the resin particle may be 95% by weight or more, based onthe total weight of the first surfactant contained in the resinparticle.

The content of the second surfactant at the core of the resin particlemay be 95% by weight or more, based on the total weight of the secondsurfactant contained in the resin particle. Further, the content of thesecond surfactant farther away from two-thirds of the particle radiusfrom the core of the resin particle may be less than 5% by weight, basedon the total weight of the second surfactant contained in the resinparticle.

Meanwhile, the resin particle may contain 1 to 20 parts by weight of thefirst surfactant and 1 to 20 parts by weight of the second surfactant,based on 100 parts by weight of the polyalkylene carbonate resin.

Further, a weight ratio of the second surfactant to the first surfactantmay be 1:0.1 to 1:2.

Further, the resin particle may have a diameter of 200 to 600 nm.

Meanwhile, the polyalkylene carbonate resin may contain a repeating unitrepresented by the following Chemical Formula 1:

wherein n is an integer of 10 to 1000,

R¹ and R² are each independently hydrogen, an alkyl group having 1 to 20carbon atoms, an aryl group having 6 to 20 carbon atoms, an alkenylgroup having 1 to 20 carbon atoms or a cycloalkyl group having 3 to 20carbon atoms, and R¹ and R² may be connected to each other to form acycloalkyl group having 3 to 10 carbon atoms.

Further, the first surfactant may be one or more compounds selected fromthe group consisting of anionic surfactants and nonionic surfactants.

Further, the second surfactant may be one or more compounds selectedfrom the group consisting of alcohols having 10 to 40 carbon atoms,alkanes, mercaptans, carboxylic acids, ketones, amines, and nonionicsurfactants having HLB (Hydrophile-Lipophile Balance) of 11 or less.

Further, the resin particle may further contain one or more hydrophilicpolymers selected from the group consisting of cellulose, polyvinylalcohol, polyacrylic acid, and polymethacrylic acid.

The resin film has physical properties of a stress of 8 MPa or less at500% elongation, an elongation at break of 800% to 1600%, and a fracturestress of 5 to 25 MPa at a thickness of 30 to 70 μm.

Further, the resin film may be a disposable glove, a disposablecontainer or a rubber molded product.

Meanwhile, according to the present invention, provided is a method formanufacturing the polyalkylene carbonate-based resin film including thesteps of:

preparing an oil-in-water emulsion composition including resin particlescontaining a polyalkylene carbonate resin, a first surfactant, and asecond surfactant, in which the second surfactant concentration ishigher at the core of the particle than at the surface of the particleand the first surfactant concentration is higher at the surface of theparticle than at the core of the particle;

forming a coating layer containing the composition; and

drying the coating layer.

Herein, the step of preparing the emulsion may include the steps ofpreparing an organic solution containing the polyalkylene carbonateresin, the second surfactant and an organic solvent; preparing anaqueous solution containing the first surfactant; and mixing the organicsolution and the aqueous solution.

Further, the step of mixing the organic solution and the aqueoussolution may include the steps of adding the aqueous solution to theorganic solution to form a water-in-oil (W/O) emulsion composition; andincreasing the supply of the aqueous solution to convert thewater-in-oil (W/O) emulsion composition into the oil-in-water (O/W)emulsion composition by phase inversion.

Meanwhile, the solid content of the emulsion composition may be 10 to50% by weight, based on the total weight of the composition. Further,the emulsion composition may have a viscosity of 1 to 70 cP.

Advantageous Effects

The polyalkylene carbonate-based resin film according to the presentinvention has biodegradability and complete combustion decomposabilityto show environment-friendly feature and rubber-like properties.Therefore, the resin film can be applied to various resin moldedproducts requiring elasticity, and in particular, preferably applied toresin molded products such as disposable groves, disposable containers,and disposable rubber molded products.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph (S-S curve) of tensile properties of the resin filmaccording to Example 1 of the present invention;

FIG. 2 is a graph (S-S curve) of tensile properties of the resin filmaccording to Control Example 1 of the present invention; and

FIG. 3 is a graph (S-S curve) of tensile properties of the resin filmaccording to Comparative Example 1 of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, a description will be given about a polyalkylenecarbonate-based resin film and a manufacturing method thereof accordingto the specific embodiments of the present invention.

Unless otherwise specified throughout this specification, the technicalterms used herein are only for reference to specific embodiments and isnot intended to limit the present invention. A singular form used hereinincludes a plural form unless the phrases clearly define contrarily.

Further, the term “include” specifies a specific feature, region,integer, step, action, element, or component, but does not exclude theaddition of a different specific feature, area, integer, step, action,element, component, or group.

Though terms including ordinal numbers such as “a first”, “a second”,etc. may be used to explain various components, the components are notlimited to the terms. The terms are used only for the purposed ofdistinguishing one component from another component. For instance, afirst component may be referred to as a second component, or similarly,the second component may be referred to as the first component, withoutdeparting from the scope of the present invention.

Further, the meaning that any component “substantially does not exist”in a specific region of the resin particle is construed as that thecontent of any component in the specific region of the resin particle isless than about 5% by weight, or less than about 3% by weight, or lessthan about 1% by weight, based on the total weight of any componentincluded in the resin particle.

Further, the term “disposable resin molded product” refers to anyrecycled resin molded product that is not designed for permanent orsemi-permanent use but disposed or recycled through a defined processafter single use or several times of use, for example, less than 10times, preferably less than 5 times. This disposable resin moldedproduct may include a resin layer satisfying the rubber-like elongationand strength requirements or may consist of the resin layer alone.Examples of the molded product may include a disposable glove, adisposable film, a disposable container such as a disposable cup ordish, a building material, or an automotive interior material. The useof the disposable resin molded product is not specifically limited andmay encompass a wide range of applications in the fields of medicine,chemistry, chemical engineering, or cosmetics.

On the other hand, the present inventors have studied a biodegradableresin molded product, and they have found out that an emulsioncomposition containing polyalkylene carbonate resin particles in whichdistributions of a first surfactant and a second surfactant arecontrolled is able to form a film having more improved stability.Furthermore, the resin particles contained in the emulsion compositioncan be controlled to have more uniform particle size, and thus it ispossible to provide a molded product manufactured by using the same withmore improved touch as well as more improved mechanical properties suchas tensile strength or the like, thereby completing the presentinvention.

In this regard, when the previous latex resin composition is used, aresin film can be formed by a coating method. However, since the formedresin film has low stability, there is a limit in manufacturing a moldedproduct having a complex structure, and there is a problem thatmechanical properties of the resin film are deteriorated. In contrast,because the composition applied in manufacturing the polyalkylenecarbonate-based resin film according to the present invention includesthe resin particles, the composition has excellent stability, comparedto the previous latex resin composition and it is possible to controlthe uniform size of resin particles. Therefore, a resin film having auniform thickness and excellent mechanical properties can be more stablyformed using the composition by a simple method such as dip molding orcoating.

According to one embodiment of the present invention, provided is apolyalkylene carbonate-based resin film including resin particlescontaining a polyalkylene carbonate resin, a first surfactant, and asecond surfactant, in which the second surfactant concentration ishigher at the core of the particle than at the surface of the particleand the first surfactant concentration is higher at the surface of theparticle than at the core of the particle.

That is, the polyalkylene carbonate-based resin film according to oneembodiment may be manufactured in the form of including resin particlescontaining the polyalkylene carbonate resin, the first surfactant andthe second surfactant. Preferably, the resin film can be formed from anemulsion composition containing resin particles. In the resin film, theresin particles can be included in the form of interconnected matrix dueto coagulation phenomena between particles. In this regard, the resinfilm may partially include resin particles maintaining their originalshape (for non-limiting example, in the form of having a particle corecontaining the polyalkylene carbonate resin and the second surfactantand a particle surface surrounding the core and containing the firstsurfactant).

Herein, the polyalkylene carbonate resin contained in the resinparticles is a non-crystalline transparent resin. Unlike aromaticpolycarbonate resins that are engineering plastics of a similar series,the polyalkylene carbonate resin has advantages that it is biodegradableand thermally decomposable at a low temperature, and completelydecomposed into carbon dioxide and water with no carbon residue leftbehind. In addition, the polyalkylene carbonate resin has a relativelylow glass transition temperature (Tg) below about 40° C., for example,about 10 to 40° C. as adjustable within the range (Inoue et al. PolymerJ., 1982, 14, 327-330).

In one embodiment, the polyalkylene carbonate resin is a kind ofpolycarbonate polymers prepared from an epoxide compound, for example,an alkylene oxide compound and carbon dioxide used as monomers throughcopolymerization, and can be defined as a homopolymer or copolymerincluding a repeating unit of the following Chemical Formula 1:

wherein n is an integer of 10 to 1000,

R¹ and R² are each independently hydrogen, an alkyl group having 1 to 20carbon atoms, an aryl group having 6 to 20 carbon atoms, an alkenylgroup having 1 to 20 carbon atoms or a cycloalkyl group having 3 to 20carbon atoms, and R¹ and R² are connected to each other to form acycloalkyl group having 3 to 10 carbon atoms.

The polyalkylene carbonate resin can be obtained using an epoxide-basedmonomer, for example, ethylene oxide, propylene oxide, 1-butene oxide,2-butene oxide, isobutyrene oxide, 1-pentene oxide, 2-pentene oxide,1-hexene oxide, 1-octene oxide, cyclopentene oxide, cyclohexene oxide,styrene oxide, or butadiene monoxide, or using two or more of thedifferent epoxide-based monomers.

To maintain the characteristic properties pertaining to the repeatingunit, the polyalkylene carbonate resin may be a homopolymer consistingof the repeating unit, or a copolymer containing the repeating unit. Forexample, the polyalkylene carbonate resin may be a copolymer of two ormore repeating units belonging to the category of Chemical Formula 1, ora copolymer containing the repeating unit and an alkylene oxideresin-based repeating unit. In order to maintain the characteristicproperties pertaining to the repeating unit of Chemical Formula 1, forexample, biodegradability or low glass transition temperature, thepolyalkylene carbonate resin can be a copolymer containing one or moreof the repeating unit of Chemical Formula 1 in an amount of about 40mole % or more, preferably about 60 mole % or more, and more preferablyabout 80 mole % or more.

Further, the repeating unit of Chemical Formula 1 includes differentfunctional groups as substituents, such as hydrogen, an alkyl grouphaving 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms,an alkenyl group having 1 to 20 carbon atoms, or a cycloalkyl grouphaving 3 to 20 carbon atoms. Among these functional groups, a proper oneis selected as a substituent in consideration of the mechanicalproperties or biodegradability of a desired polyalkylene carbonateresin. For example, the polyalkylene carbonate resin including therepeating unit of Chemical Formula 1 is superior in terms ofbiodegradability when the substituent is a hydrogen atom or a functionalgroup containing a relatively small number of carbon atoms (e.g., analkyl or cycloalkyl group having a small number of carbon atoms) as asubstituent; or superior in terms of mechanical properties such asstrength when the substituent is a functional group containing arelatively large number of carbon atoms. For specific example, it wasreported that the polyethylene carbonate resin is biodegraded morerapidly than the polypropylene carbonate resin (Inoue et al. Chem.Pharm. Bull, Jpn, 1983, 31, 1400; Ree et al. Catalysis Today, 2006, 115,288-294).

In the polyalkylene carbonate resin, the degree of polymerization (n) ofthe repeating unit of Chemical Formula 1 may be 10 to 1000, andpreferably 50 to 500. The polyalkylene carbonate resin containing thesame may have a weight average molecular weight of about 10,000 to1,000,000, and preferably, about 50,000 to 500,000. As the repeatingunit and the polyalkylene carbonate resin have a degree ofpolymerization and a weight average molecular weight in such ranges, theresin layer or the disposable resin molded product manufactured from thesame can have biodegradability as well appropriate mechanical propertiessuch as strength.

According to one embodiment, the resin particle may further include ahydrophilic polymer typically used in the art pertaining to the presentinvention, in addition to the polyalkylene carbonate resin. Thehydrophilic polymer makes properties of the composition including theresin particles more uniform when the composition is applied.Non-limiting example of the hydrophilic polymer may be one or morecompounds selected from the group consisting of cellulose, polyvinylalcohol, polyacrylic acid, and poly methacrylic acid. However, thecontent of the hydrophilic polymer may be determined considering itseffects on biodegradability and mechanical properties of the resin filmrequired in the present invention, and for example, the content may be20 parts by weight or less, preferably 0.01 to 20 parts by weight, andmore preferably 0.1 to 10 parts by weight, based on 100 parts by weightof the polyalkylene carbonate resin.

Meanwhile, the resin particles included in the resin film of oneembodiment include the first surfactant and the second surfactanttogether with the above mentioned polyalkylene carbonate resin.

In particular, the first surfactant and the second surfactant havedifferent concentration distributions at the core and surface of theresin particle. According to one embodiment, the first surfactantconcentration is higher at the surface of the resin particle than at thecore of resin particle. On the contrary, the second surfactantconcentration is higher at the core of the resin particle than at thesurface of resin particle. Furthermore, the first surfactant may notsubstantially exist at the core of the resin particle and the secondsurfactant may not substantially exist at the surface of the resinparticle.

Herein, the “core” of the resin particle means the region withintwo-thirds of the radius from the center of the resin particle or theregion within half the radius from the center of the resin particle.Further, the “surface” of the resin particle means a region excludingthe core from the resin particle.

The meaning that the first or second surfactant “substantially does notexist” in a specific region of the resin particle is construed as thatthe content of the first or second surfactant in the specific region ofthe resin particle is less than about 5% by weight, or less than about3% by weight, or less than about 1% by weight, based on the total weightof the first or second surfactant included in the resin particle.

In other words, the first surfactant may not exist in the region withinhalf or two-thirds of the radius of the resin particle from the centerof the resin particle. In other region (that is, surface of the resinparticle), about 95% by weight or more of the first surfactant containedin the resin particle may be included. Further, the second surfactantmay not substantially exist in the region (that is, surface of the resinparticle) farther away from half or two-thirds of the radius of theresin particle from the center of the resin particle. In the core of theresin particle, about 95% by weight or more of the second surfactantcontained in the resin particle may be included, together with thepolyalkylene carbonate resin.

As described above, the resin particles included in the resin filmaccording to one embodiment may have the particle core containing thepolyalkylene carbonate resin and the second surfactant and the particlesurface surrounding the core and containing the first surfactant. Thesecond surfactant does not substantially exist at the surface of theparticle, and the first surfactant does not exist deeper than apredetermined depth of the resin particle.

As such, because the concentration distributions of the first surfactantand the second surfactant are controlled within the resin particle, thepolyalkylene carbonate resin can exist as a particle having a morestable and uniform size, and the resin particles can be stablydistributed in the composition. Furthermore, coagulation between theresin particles is minimized, and thus high content of the effectivesolid components distributed in the composition is maintained so as toform a molded product having more uniform thickness and physicalproperties when the composition is applied.

In this connection, if the resin particles included in the emulsioncomposition are unstable, coagulation and precipitation of resinparticles may occur and therefore, the content of the effective solidcomponents distributed in the composition is decreased (herein, the‘content of the effective solid components’ means the content of theresin particles and other additives which are solid components thatstably exist in a dispersed phase within the composition and can bedirectly used in the manufacture of the resin molded product, excludingcoagulation formed by coagulation of the resin particles andprecipitates thereof). From this point of view, as the resin particlesaccording to one embodiment are formed by including the first surfactantand the second surfactant at the same time according to the abovementioned concentration distribution, the resin particles are able toform a more stable dispersed phase in the composition and coagulationbetween particles can be minimized to maintain high content of effectivesolid components dispersed in the composition. If any one of the firstsurfactant and the second surfactant is not included, or does notsatisfy the concentration distribution of the above embodiment, thecontent of effective solid components dispersed in the composition isdecreased due to coagulation between unstable resin particles, andconsequently, it is difficult to manufacture a resin molded producthaving uniform thickness and physical properties.

Herein, the presence of the first surfactant can be identified byMALDI-TOF Mass, GC/Mass, and NMR analysis of the supernatant that isobtained by centrifugation of the composition including the resinparticles. Further, the presence of the second surfactant can beidentified by MALDI-TOF Mass, GC/Mass, and NMR analysis of theprecipitate that is obtained by centrifugation of the compositionincluding the resin particles. As described below, if a water solvent isincluded in the emulsion composition, the second surfactant is lesshydrophilic than the first surfactant, and thus the second surfactanthaving relatively low hydrophilicity is distributed at the core of theresin particle, and the first surfactant having relatively highhydrophilicity is distributed at the surface of the resin particle.Therefore, it is possible to predict the structure of the resin particleincluding the first surfactant and the second surfactant.

Meanwhile, according to one embodiment, the resin film can be obtainedfrom the emulsion composition including the resin particles. Herein, ifthe emulsion composition is, for example, a water solvent, the firstsurfactant and the second surfactant are compounds showing the abovedescribed concentration distribution, and they can be determined,considering the difference in hydrophilicity. That is, the secondsurfactant is a substance having lower hydrophilicity or having lowerHLB (Hydrophile-Lipophile Balance) than the first surfactant, and it ispossible to give the above described concentration distribution.

According to one embodiment, the first surfactant may be one or morecompounds selected from the group consisting of anionic surfactants andnonionic surfactants. Preferably, the first surfactant may be one ormore compounds selected from the group consisting of carboxylic acidsalts, sulfonic acid salts, sulfuric acid ester salts, phosphoric acidester salts, quaternary ammonium salt, ether, esterether, ester,nitrogen-containing surfactants. These compounds are those typicallyused in the art pertaining to the present invention without particularlimitation. However, according to one embodiment, the first surfactantmay be an anionic surfactant such as alkyl benzene sodium sulfonate,alkyl sodium sulfonate, polyethylene oxide alkyl ether, polyethyleneoxide alkyl phenyl ether, polyethylene oxide alkyl ether sulfonate,polyethylene oxide alkyl ether phosphate, sodium lauryl sulfate,alkylether carbonate, alkylether sulfate, alkylaryl ether sulfate,alkylamide sulfate, alkyl phosphate, alkylether phosphate, and alkylarylether phosphate; a nonionic surfactant such as alkyl polyoxyethyleneether, alkylaryl polyoxyethylene ether, alkylaryl formaldehyde condensedpolyoxyethylene ether, a block copolymer of hydrophobicpolyoxypropylene, polyoxyethylene ether of glycerin ester,polyoxyethylene ether of sorbitan ester, polyoxyethylene ether ofsorbitol ester, polyethylene glycol fatty acid ester, glycerin ester,sorbitan ester, propylene glycol ester, sugar ester, fatty acidalkanolamide, polyoxyethylene fatty acid amide, polyoxyethylene alkylamine, and amine oxide; or a mixture thereof.

The first surfactant may be included in an amount of 1 to 20 parts byweight, preferably 1 to 15 parts by weight, and more preferably 1 to 10parts by weight, based on 100 parts by weight of the above describedpolyalkylene carbonate resin. That is, it is preferable that the contentof the first surfactant is within the above range, consideringsufficient formation of the surface surrounding the core of the resinparticle, and problems such as reduction in the processability andmechanical properties of the resin molded product generated by excessiveaddition of the first surfactant.

Meanwhile, the second surfactant reduces water solubility of the resinparticles present in the solvent to prevent coagulation between resinparticles, and as described above, its type can be selected consideringthe relationship with the first surfactant. Non-limiting examples of thesecond surfactant may be one or more compounds selected from the groupconsisting of alcohols having 10 to 40 carbon atoms, alkanes,mercaptans, carboxylic acids, ketones, amines and nonionic surfactantshaving HLB (Hydrophile-Lipophile Balance) of 11 or less. Preferably, thesecond surfactant may be hexadecane, cetyl alcohol, polyoxyethylenestearyl ether, polyoxyethylene stearyl amine, polyoxyethylene stearylester, polyoxyethylene monostearate, polyoxyethylene sorbitanmonooleate, polyoxyethylene lauryl ether, ethoxylated alcohols having 10to 20 carbon atoms, ethoxylated octylphenol, ethoxylated fatty acidester, sorbitan laurate, sorbitan monostearate, propylene glycolmonostearate, ethylene glycol monostearate, sorbitan fatty acid ester,polyoxyethylene sorbitan fatty acid ester or a mixture thereof.

The second surfactant may be included in an amount of 1 to 20 parts byweight, preferably 1 to 15 parts by weight, and more preferably 1 to 10parts by weight, based on 100 parts by weight of the above describedpolyalkylene carbonate resin. That is, it is preferable that the contentof the second surfactant is within the above range, considering morestable formation of the resin particles, difficulties in the control ofthe particle size and the composition stability which are generated byexcessive addition of the second surfactant, and changes in the physicalproperties of the resin molded product.

Furthermore, in order to form and maintain more stable resin particles,a weight ratio of the second surfactant to the first surfactant can becontrolled to be 1:0.1 to 1:2, preferably 1:0.2 to 1:1, and morepreferably 1:0.3 to 1:0.6.

Meanwhile, the resin particle may have a diameter of 200 to 600 nm,preferably 250 to 600 nm, and more preferably 250 to 550 nm. That is, itis preferable that the diameter of the resin particle satisfies theabove range, in order to maintain the content of the effective solidcomponents included in the emulsion composition and to form a filmhaving a uniform thickness during manufacture of the resin moldedproduct. If the diameter of the resin particle does not satisfies theabove described range (e.g., the diameter exceeds 600 nm), stability ofthe resin particle is reduced, and thus it is difficult to securesufficient content of the solid components included in the emulsioncomposition, and it is also difficult to form a resin molded producthaving a uniform thickness and physical properties by using the same.

As such, the resin film according to one embodiment is advantageous inthat it can be elongated at a high rate with a low stress, compared tothe previous latex films (e.g., nitrile-based films) and has excellentmechanical properties such as higher maximum elongation.

According to one embodiment, the polyalkylene carbonate-based resin filmhas physical properties of a stress of 8 MPa or less at 500% elongation,an elongation at break of 800% to 1600%, and a fracture stress of 5 to25 MPa at a thickness of 30 to 70 μm.

As shown in comparison of FIGS. 1 and 2, the resin film of oneembodiment (FIG. 1: S-S curve of the resin film according to Example 1)has a stress of 8 MPa or less at 500% elongation at a thickness of about55 μm, whereas the previous nitrile latex films (FIG. 2: S-S curve ofthe resin film according to Control Example 1) has a stress of about 25MPa at 500% elongation, and thus it can be elongated at a higher ratewith a lower stress.

This physical property is closely related to wearing comfort of thedisposable resin molded products, in particular, disposable gloves. Asthe resin film of one embodiment can be elongated at a high rate with alower stress, it is able to exhibit advantages of excellent elasticityand wearing comfort.

Further, according to one embodiment, the resin film has physicalproperty of a stress of 2 to 8 MPa at 300% to 500% elongation at athickness of 30 to 70 μm; preferably a stress of 4 to 8 MPa at 300% to500% elongation at a thickness of 40 to 60 μm.

Furthermore, according to another embodiment, the resin film hasphysical property of a stress of 2 to 6 MPa at 300% elongation at athickness of 30 to 70 μm; preferably a stress of 4 to 6 MPa at 300%elongation at a thickness of 40 to 60 μm.

Furthermore, according to still another embodiment, the resin film hasphysical property of a stress of 3 to 8 MPa at 500% elongation at athickness of 30 to 70 μm; preferably a stress of 5 to 8 MPa at 500%elongation at a thickness of 40 to 60 μm.

Furthermore, the resin film has physical properties of an elongation atbreak of 800% to 1600%, preferably 800% to 1300%, and more preferably800% to 1000%; and a fracture stress of 5 to 25 MPa, preferably 10 to 20MPa, and more preferably 10 to 15 MPa at a thickness of 30 to 70 μm.That is, the resin film of one embodiment is able to exhibit excellentrubber elasticity as well as high durability, and these physicalproperties have never been achieved by the previous nitrile-based filmsor biodegradable films.

As such, the resin film according to the present invention hasrubber-like properties and also has biodegradability and completecombustion decomposability of the polyalkylene carbonate resin, and thusthe resin film can be suitably used for, in particular, the disposableresin molded products requiring rubber elasticity. Herein, thedisposable resin molded product may include the resin film of oneembodiment or may consist of the resin film alone. Examples of themolded product include disposable rubber or resin molded productscombustible in incineration such as disposable gloves, disposable films,disposable containers such as disposable cups or plates, and buildingmaterials or automotive interior materials. The use of the disposableresin molded product is not particularly limited, and may encompass awide range of applications in the fields of medicine, chemistry,chemical engineering, food or cosmetics.

On the other hand, according to another embodiment of the presentinvention, provided is a method for manufacturing the polyalkylenecarbonate-based resin film including the steps of:

preparing an oil-in-water emulsion composition containing the resinparticles;

forming a coating layer containing the composition; and

drying the coating layer.

Herein, the resin particles are those containing the polyalkylenecarbonate resin, the first surfactant and the second surfactant, inwhich the second surfactant concentration is higher at the core of theparticle than at the surface of the particle and the first surfactantconcentration is higher at the surface of the particle than at the coreof the particle.

In one embodiment, the emulsion composition may be an oil-in-wateremulsion composition containing a water-containing continuous phase andresin particles dispersed in the continuous phase.

The emulsion composition can be prepared according to a preparationmethod of an oil-in-water emulsion composition typically used in the artpertaining to the present invention, for example, direct emulsificationor phase inversion emulsification, except that the above describedpolyalkylene carbonate resin, the first surfactant, and the secondsurfactant are used.

According to one embodiment, the step of preparing the emulsioncomposition may be performed by a method including the steps ofpreparing an organic solution containing the polyalkylene carbonateresin, the second surfactant and the organic solvent; preparing anaqueous solution containing the first surfactant; and mixing the organicsolution and the aqueous solution. Further, if the phase inversionemulsification is performed, the step of mixing the organic solution andthe aqueous solution may be performed by a method including the steps ofadding the aqueous solution to the organic solution to form awater-in-oil (W/O) emulsion composition; and increasing the supply ofthe aqueous solution to convert the water-in-oil (W/O) emulsioncomposition into the oil-in-water (O/W) emulsion composition by phaseinversion.

Meanwhile, the types and contents of the polyalkylene carbonate resin,the first surfactant, and the second surfactant used in the preparationof the emulsion composition are the same as described above.

The organic solvent included in the emulsion composition may be selectedfrom the typical solvents in which the polyalkylene carbonate resin canbe dissolved, and the constitution is not particularly limited. However,according to one embodiment, the organic solvent may be one or moresolvents selected from the group consisting of methyl acetate, ethylacetate, propyl acetate, isopropyl acetate, vinyl acetate, methyl ethylketone, dichloromethane, dichloroethane, chloroform, acetonitrile,methylpyrrolidone, dimethyl sulfoxide, nitromethane, nitropropane,caprolactone, acetone, polypropylene oxide, tetrahydrofuran, benzene,and styrene. Further, the content of the organic solvent may bedetermined, considering formation efficiency and stability of the resinparticles. For non-limiting example, the organic solvent may be includedin an amount of 50 to 1000 parts by weight, preferably 100 to 1000 partsby weight, and more preferably 200 to 1000 parts by weight, based on 100parts by weight of the polyalkylene carbonate resin.

At this time, the solid content of the emulsion composition is 10 to 50%by weight, preferably 10 to 40% by weight, and more preferably 10 to 30%by weight, based on the total weight of the composition, which isadvantageous in terms of processability of the resin molded product. Theviscosity of the emulsion composition is 1 to 70 cP, preferably 1 to 50cP, and more preferably 2 to 30 cP, which is advantageous in terms ofprocessability.

In addition, the emulsion composition may further include additives suchas an antifoaming agent, a hydrophilic polymer or the like in order tosecure more uniform physical properties upon applying the composition.At this time, the antifoaming agent may be those typically used in theart pertaining to the present invention, and the constitution is notparticularly limited, but a silicone-based antifoaming agent ispreferred. The antifoaming agent may be added in an amount of 0.001 to0.1 parts by weight, based on the total weight of the composition.

Meanwhile, the manufacturing method of the resin film according to oneembodiment includes the steps of forming a coating layer containing thecomposition using the emulsion composition prepared by the abovedescribed method; and drying the coating layer.

Of them, the step of forming the coating layer containing thecomposition may be performed by a method of coating a mold or substratehaving the shape of the desired molded product with the emulsioncomposition at a predetermined thickness. At this time, the method ofcoating the composition may be performed by a method typically used inthe art pertaining to the present invention, and is not particularlylimited.

The step of drying the coating layer is a step of forming a resin filmby evaporating the solvent such as moisture contained in the coatinglayer. Preferably, the step may be performed at a temperature to form aresin film having uniform physical properties due to coagulationphenomena between the resin particles, for example, at a temperature of70 to 160° C., or 90 to 140° C., or 100 to 130° C.

Hereinafter, the preferred Examples are provided for betterunderstanding. However, the following Examples are for illustrativepurposes only, and the invention is not intended to be limited by theseExamples.

Preparation Example 1 Preparation of Polypropylene Carbonate Resin

A zinc-glutarate (Zn-glutarate) catalyst was used in copolymerizingpropylene oxide and carbon dioxide to prepare a polypropylene carbonateresin according to the following method (Polymer Journal 1981, 13, 407;U.S. Pat. No. 5,026,676).

Dry zinc-glutarate catalyst (1 g) and purified propylene oxide (30 g)were put into an autoclave reactor equipped with an agitator, and thereactor was purged with carbon dioxide under about 10 atm and thenstirred for 10 minutes. The reactor was purged again with carbon dioxideunder about 50 atm and then allowed to warm up to 60° C. for about 24hours of reaction. After completion of the reaction, unreacted propyleneoxide was removed under reduced pressure and dissolved indichloromethane solvent. The solution was washed with an aqueous HClsolution (0.1 M) and precipitated with a methanol solvent to yield apolypropylene carbonate resin. The collected resin was about 25 g andidentified by a nuclear magnetic resonance spectrum. The weight averagemolecular weight of the resin as measured by GPC was 250,000.

Preparation Example 2 Preparation of Polyethylene Carbonate Resin

Diethyl-zinc catalyst was used in copolymerizing ethylene oxide andcarbon dioxide to prepare a polyethylene carbonate resin according tothe following method (Journal of Polymer Science B 1969, 7, 287; Journalof Controlled release 1997, 49, 263).

Dry diethyl-zinc catalyst (1 g) and dioxane solvent (10 mL) were putinto an autoclave reactor equipped with an agitator. To this was addeddioxane solvent (5 mL) diluted with purified water (0.1 g) while thereactor were being stirred slowly. The reactor was purged with carbondioxide under about 10 atm and then stirred at 120° C. for 1 hour.Purified ethylene oxide (10 g) was added. The reactor was purged againwith carbon dioxide under about 50 atm and then allowed to warm up to60° C. for about 48 hours of reaction. After completion of the reaction,unreacted ethylene oxide was removed under reduced pressure anddissolved in dichloromethane solvent. The solution was washed with anaqueous HCl solution (0.1 M) and precipitated with a methanol solvent toyield a polyethylene carbonate resin. The collected resin was about 15 gand identified by a nuclear magnetic resonance spectrum. The weightaverage molecular weight of the resin as measured by GPC was 230,000.

[Experimental Method]

In the following Examples and Comparative Examples, all the experimentsdealing with air- or water-sensitive compounds were carried out usingstandard Schlenk or dry box techniques.

1) Nuclear magnetic resonance spectra were obtained with a Bruker 600spectrometer, and 1H NMR was measured at 600 MHz.

2) Weight average molecular weight of the polymer was measured by GPC(gel permeation chromatography), and a polystyrene sample was used as astandard.

3) For measurement of the solid content in the composition, a HalogenMoisture Analyzer (HB43-S.Mettler Toledo) was used, and moisture andother solvents were evaporated at a temperature of about 110° C. and theweight of the residual solid components was measured.

4) Size of the resin particles contained in the composition was measuredusing a particle size analyzer (NICOMP380) at a temperature of about 23°C.

5) Presence of the first surfactant and the second surfactant in theresin particles was identified by MALDI-TOF Mass of the supernatant andthe precipitate obtained from centrifugation of the emulsioncomposition.

6) Viscosity of the composition was measured using Brookfield LV at atemperature of about 23° C.

Example 1 Preparation of Emulsion Composition for Preparation ofPolyalkylene Carbonate Molded Product

About 720 g of dichloromethane, about 2.6 g of hexadecane (secondsurfactant), and about 80 g of the polyethylene carbonate resinaccording to Preparation Example 2 were mixed and solid components weredissolved to prepare an organic solution.

Separately, about 5.2 g of sodium dodecyl benzene sulfonate was added toabout 300 g of distilled water, and stirred to prepare an aqueoussolution containing the first surfactant.

The organic solution was slowly added to the aqueous solution understirring at about 10,000 rpm for about 20 minutes for stabilization toprepare an emulsion composition containing resin particles. Thereafter,dichloromethane was separated from the emulsion composition using arotary evaporator to prepare a final polyethylene carbonate emulsioncomposition.

At this time, it was confirmed that the solid content of the compositionwas about 25% by weight, the diameter of the resin particle was about280 to 320 nm, and the viscosity of the composition was about 4.5 cP.

Presence of the first surfactant and the second surfactant in the resinparticles was identified by MALDI-TOF Mass of the supernatant and theprecipitate obtained from centrifugation of the emulsion composition. Atthis time, it was found that the first surfactant corresponding to about97% by weight of the total content of the added first surfactant and thesecond surfactant of less than about 1% by weight were contained in thesupernatant. It was also found that the second surfactant correspondingto about 99% by weight of the total content of the added secondsurfactant and the first surfactant of less than about 3% by weight werecontained in the precipitate. Referring to the analysis result anddifference in hydrophilicity between the first surfactant and the secondsurfactant, it could be expected that the resin particle was formed tohave a structure of containing the polyethylene carbonate resin and thesecond surfactant at its core and the first surfactant at its surface.

Further, it was found that the coagulation formed at about 24 hoursafter preparation of the emulsion composition was about 4% by weight,based on the total solid components.

Formation of Polyalkylene Carbonate-Based Resin Film

A calcium nitrate-coated glass mold was dipped in the emulsioncomposition for about 15 seconds, and then moisture was dried at about130° C. to form a resin film. Thereafter, leaching was performed usingrunning water for about 1 minute, and then moisture was dried at about130° C. to form a resin film having a thickness of about 55 μm.

Example 2 Preparation of Emulsion Composition for Preparation ofPolyalkylene Carbonate Molded Product

An emulsion composition was prepared under the same conditions and inthe same manner as in Example 1, except that the content of hexadecane(second surfactant) was controlled to about 5.2 g during preparation ofthe organic solution.

At this time, it was confirmed that the solid content of the compositionwas about 25% by weight, the diameter of the resin particle was about300 to 350 nm, and the viscosity of the composition was about 4.5 cP.

Formation of Polyalkylene Carbonate-Based Resin Film

A resin film having a thickness of about 55 μm was obtained in the samemanner as in Example 1, except for using the above emulsion composition.

Example 3 Preparation of Emulsion Composition for Preparation ofPolyalkylene Carbonate Molded Product

An emulsion composition was prepared under the same conditions and inthe same manner as in Example 1, except that about 0.4 g of ahydrophilic polymer, sodium carboxymethyl cellulose was further addedduring preparation of the organic solution.

At this time, it was confirmed that the solid content of the compositionwas about 25% by weight, the diameter of the resin particle was about300 to 400 nm, and the viscosity of the composition was about 21 cP.

Formation of Polyalkylene Carbonate-Based Resin Film

A resin film having a thickness of about 55 μm was obtained in the samemanner as in Example 1, except for using the above emulsion composition.

Example 4 Preparation of Emulsion Composition for Preparation ofPolyalkylene Carbonate Molded Product

About 720 g of dichloromethane, about 2.6 g of hexadecane (secondsurfactant), and about 80 g of the polyethylene carbonate resinaccording to Preparation Example 2 were mixed and solid components weredissolved to prepare an organic solution.

Separately, about 5.2 g of sodium dodecyl benzene sulfonate was added toabout 300 g of distilled water, and stirred to prepare an aqueoussolution containing the first surfactant.

The aqueous solution was slowly added to the organic solution understirring at about 10,000 rpm to induce phase inversion. After phaseinversion, the mixture was stirred at about 10,000 rpm for about 5minutes for stabilization to prepare an emulsion composition containingresin particles. Thereafter, dichloromethane was separated from theemulsion composition using a rotary evaporator to prepare a finalpolyethylene carbonate emulsion composition.

At this time, it was confirmed that the solid content of the compositionwas about 25% by weight, the diameter of the resin particle was about350 to 500 nm, and the viscosity of the composition was about 4.5 cP.Presence of the first surfactant and the second surfactant in the resinparticles was identified by MALDI-TOF Mass of the supernatant and theprecipitate obtained from centrifugation of the emulsion composition.Referring to difference in hydrophilicity between the first surfactantand the second surfactant, it could be expected that the resin particlewas formed to have a structure of containing the polyethylene carbonateresin and the second surfactant at its core and the first surfactant atits surface.

Formation of Polyalkylene Carbonate-Based Resin Film

A resin film having a thickness of about 50 μm was obtained in the samemanner as in Example 1, except for using the above emulsion composition.

Comparative Example 1 Preparation of Emulsion Composition forPreparation of Polyalkylene Carbonate Molded Product

An emulsion composition was prepared under the same conditions and inthe same manner as in Example 1, except that no hexadecane (secondsurfactant) was added during preparation of the organic solution.

At this time, it was confirmed that the solid content of the compositionwas about 25% by weight, the diameter of the resin particle was about650 to 800 nm, and the viscosity of the composition was about 4.5 cP.Further, it was found that the coagulation formed at about 24 hoursafter preparation of the emulsion composition was about 18% by weight,based on the total solid components.

Formation of Polyalkylene Carbonate-Based Resin Film

A resin film having a thickness of about 50 μm was obtained in the samemanner as in Example 1, except for using the above emulsion composition.

Control Example 1 Preparation of Nitrile Latex Composition

A high-pressure reactor which was equipped with an agitator, athermometer, a cooler, an inlet tube for a nitrogen gas and equipped soas to continuously introduce raw materials was prepared. Air inside thereactor was replaced by nitrogen gas, and then 2 parts by weight ofalkyl benzene sodium sulfonate, 0.5 parts by weight of t-dodecylmercaptan and 140 parts by weight of ion exchanged water were injected,based on 100 parts by weight of monomer mixture containing 30% by weightof acrylonitrile, 66% by weight of 1,4-butadiene, and 4% by weight ofmethacrylic acid, and the temperature was raised to about 40° C.

After the temperature was raised, 0.3 parts by weight of apolymerization initiator, potassium persulfate was added. When aconversion rate reached 95%, 0.1 parts by weight of sodiumdimethyldithiocarbamate was injected to terminate the polymerization.Subsequently, unreacted monomers were removed through a deodorizationprocess and a nitrile latex composition was obtained by adding ammoniawater, an antioxidant, an antifoaming agent or the like.

Formation of Nitrile Latex Film

A latex film having a thickness of about 55 μm was obtained under thesame conditions and in the same manner as in Example 1, except for usingthe above nitrile latex composition.

Experimental Example 1

Three or four dumbbell-shaped test specimens were made using each of theresin films manufactured in Examples and Comparative Examples accordingto ASTM D 412. Using a Zwick/Z010 model (manufactured by Zwick/RoellInc.), tensile strength (MPa), elongation (%), elastic modulus(E-Modulus), modulus of elasticity at 300% elongation and modulus ofelasticity at 500% elongation of each resin film were measured at a rateof 500 mm/min.

The content of the polymer coagulation produced at 24 hours afterpreparation of the emulsion composition was measured. When the contentis 5% by weight or less, it was evaluated as ‘good’, when the content ismore than 5% by weight and 10% by weight or less, it was evaluated as‘fair’, and when the content is more than 10% by weight, it wasevaluated as ‘poor’.

The results of measuring the physical properties are summarized in thefollowing Table 1, and S-S curves of the resin films of Example 1,Control Example 1, and Comparative Example 1 are shown in FIGS. 1 to 3,respectively. Herein, the graphs of FIGS. 1˜3 show the results ofmeasuring those of each one sample (FIG. 1: resin film of Example 1,FIG. 2: resin film of Control Example 1, FIG. 3: resin film ofComparative Example 1) three˜four times, and in the following Table 1,mean values of the measured data are shown.

For comparison, physical properties of the resin film having the samethickness and consisting of a polyvinyl chloride resin or natural rubberthat has been typically used for manufacturing the conventionaldisposable resin molded products were measured in the same manner, andalso shown in the following Table 1.

TABLE 1 Modulus at Tensile 300% strength Elongation elongation Modulusat 500% Emulsion stability (MPa) (%) (MPa) elongation (MPa) (coagulationwt %) Example 1 16 1265 3.8 4.8 Good (4) Example 2 11 1430 2.8 3.5 Good(4) Example 3 13 1407 3.2 4.0 Good (2 or less) Example 4 12 853 3.8 4.9Fair (5~8) Comparative 7 1015 3.1 3.8 Poor (18) Example 1 Control 28 5869.6 20.9 — Example 1 PVC 14 550 8.3 12.6 — Natural 25 1047 2.5 5.0 —rubber

Referring to the experimental results, it was confirmed that resin filmsaccording to Examples 1 to 4 showed rubber-like elasticity and moreexcellent elongation than the nitrile resin film (Control Example 1)which have been applied to the conventional disposable resin moldedproducts, in particular, much lower stress at 300% and 500% than thenitrile resin film. Further, because the films according to Examples 1to 4 have excellent touch, it is possible to manufacture high-qualitymolded products.

In contrast, the resin film according to Comparative Example 1 showedlow tensile strength and elongation, compared to the films of Examples.In particular, stability of the emulsion composition was very low, andthe content of effective solid components in the composition was low.The thickness of the formed film was not uniform, and therefore, it isimpossible to manufacture a stable resin molded product.

1. A polyalkylene carbonate-based resin film, comprising resin particlesincluding a polyalkylene carbonate resin, a first surfactant, and asecond surfactant, wherein the second surfactant concentration is higherat the core of the particle than at the surface of the particle and thefirst surfactant concentration is higher at the surface of the particlethan at the core of the particle.
 2. The polyalkylene carbonate-basedresin film according to claim 1, wherein the content of the firstsurfactant at the core of the resin particle is less than 5% by weight,based on the total weight of the first surfactant included in the resinparticle.
 3. The polyalkylene carbonate-based resin film according toclaim 1, wherein the content of the first surfactant farther away fromhalf the particle radius from the center of the resin particle is 95% byweight or more, based on the total weight of the first surfactantincluded in the resin particle.
 4. The polyalkylene carbonate-basedresin film according to claim 1, wherein the content of the secondsurfactant at the core of the resin particle is 95% by weight or more,based on the total weight of the second surfactant included in the resinparticle.
 5. The polyalkylene carbonate-based resin film according toclaim 1, wherein the content of the second surfactant farther away fromtwo-thirds of the particle radius from the center of the resin particleis less than 5% by weight, based on the total weight of the secondsurfactant included in the resin particle.
 6. The polyalkylenecarbonate-based resin film according to claim 1, wherein the resinparticle includes 1 to 20 parts by weight of the first surfactant and 1to 20 parts by weight of the second surfactant, based on 100 parts byweight of the polyalkylene carbonate resin.
 7. The polyalkylenecarbonate-based resin film according to claim 1, wherein a weight ratioof the second surfactant to the first surfactant is 1:0.1 to 1:2.
 8. Thepolyalkylene carbonate-based resin film according to claim 1, whereinthe resin particle has a diameter of 200 to 600 nm.
 9. The polyalkylenecarbonate-based resin film according to claim 1, wherein thepolyalkylene carbonate resin includes a repeating unit represented bythe following Chemical Formula 1:

wherein n is an integer of 10 to 1000, R¹ and R² are each independentlyhydrogen, an alkyl group having 1 to 20 carbon atoms, an aryl grouphaving 6 to 20 carbon atoms, an alkenyl group having 1 to 20 carbonatoms, or a cycloalkyl group having 3 to 20 carbon atoms, and R¹ and R²are connected to each other to form a cycloalkyl group having 3 to 10carbon atoms.
 10. The polyalkylene carbonate-based resin film accordingto claim 1, wherein the polyalkylene carbonate resin has a weightaverage molecular weight of 10,000 to 1,000,000.
 11. The polyalkylenecarbonate-based resin film according to claim 1, wherein the firstsurfactant is one or more compounds selected from the group consistingof anionic surfactants and nonionic surfactants.
 12. The polyalkylenecarbonate-based resin film according to claim 1, wherein the firstsurfactant is one or more compounds selected from the group consistingof carboxylic acid salts, sulfonic acid salts, sulfuric acid estersalts, phosphoric acid ester salts, quaternary ammonium salt, ether,esterether, ester, and nitrogen-containing surfactants.
 13. Thepolyalkylene carbonate-based resin film according to claim 1, whereinthe second surfactant is one or more compounds selected from the groupconsisting of alcohols having 10 to 40 carbon atoms, alkanes,mercaptans, carboxylic acids, ketones, amines, and nonionic surfactantshaving HLB (Hydrophile-Lipophile Balance) of 11 or less.
 14. Thepolyalkylene carbonate-based resin film according to claim 1, whereinthe resin particle further includes one or more hydrophilic polymersselected from the group consisting of cellulose, polyvinyl alcohol,polyacrylic acid, and polymethacrylic acid.
 15. The polyalkylenecarbonate-based resin film according to claim 1, wherein a stress is 8MPa or less at 500% elongation, an elongation at break is 800% to 1600%,and a fracture stress is 5 to 25 MPa at a thickness of 30 to 70 μm. 16.The polyalkylene carbonate-based resin film according to claim 1,wherein a stress is 2 to 8 MPa at 300% to 500% elongation at a thicknessof 30 to 70 μm.
 17. The polyalkylene carbonate-based resin filmaccording to claim 1, wherein a stress is 2 to 6 MPa at 300% elongationat a thickness of 30 to 70 μm.
 18. The polyalkylene carbonate-basedresin film according to claim 1, wherein a stress is 3 to 8 MPa at 500%elongation at a thickness of 30 to 70 μm.
 19. The polyalkylenecarbonate-based resin film according to claim 1, wherein thepolyalkylene carbonate-based resin film is used for disposable groves,disposable containers, or disposable rubber molded products.
 20. Amethod for manufacturing the polyalkylene carbonate-based resin film,comprising the steps of: preparing an oil-in-water emulsion compositionincluding resin particles containing a polyalkylene carbonate resin, afirst surfactant, and a second surfactant, wherein the second surfactantconcentration is higher at the core of the particle than at the surfaceof the particle and the first surfactant concentration is higher at thesurface of the particle than at the core of the particle; forming acoating layer containing the composition; and drying the coating layer.21. The method according to claim 20, wherein the step of preparing theemulsion composition includes the steps of: preparing an organicsolution containing the polyalkylene carbonate resin, the secondsurfactant and the organic solvent; preparing an aqueous solutioncontaining the first surfactant; and mixing the organic solution and theaqueous solution.
 22. The method according to claim 21, wherein the stepof mixing the organic solution and the aqueous solution includes thesteps of: adding the aqueous solution to the organic solution to form awater-in-oil emulsion composition; and increasing the supply of theaqueous solution to convert the water-in-oil emulsion composition intoan oil-in-water emulsion composition by phase inversion.
 23. The methodaccording to claim 21, wherein the organic solvent is one or moreselected from the group consisting of methyl acetate, ethyl acetate,propyl acetate, isopropyl acetate, vinyl acetate, methyl ethyl ketone,dichloromethane, dichloroethane, chloroform, acetonitrile,methylpyrrolidone, dimethyl sulfoxide, nitromethane, nitropropane,caprolactone, acetone, polypropylene oxide, tetrahydrofuran, benzene,and styrene.
 24. The method according to claim 20, wherein the solidcontent of the emulsion composition is 10 to 50% by weight, based on thetotal weight of the composition.
 25. The method according to claim 20,wherein the emulsion composition has a viscosity of 1 to 70 cP.
 26. Themethod according to claim 20, wherein the drying of the coating layer isperformed at a temperature of 70 to 160° C.